Phosphorous containing zeolite having MFI type structure

ABSTRACT

The present invention discloses a phosphorus-containing zeolite having MFI type structure. The anhydrous composition (based on the mole ratios of oxides) of the above zeolite is 
     
         0.01-0.3Na.sub.2 O.Al.sub.2 O.sub.3.0.2-1.5P.sub.2 O.sub.5.30-90SiO.sub.2 
    
     Said zeolite possesses a X-ray diffraction pattern listed in Table 1. The pore volume ratio of 1.0-10 nm mesopore to 10-membered ring pore is no less than 0.5. The crystal particle size of said zeolite is in the range of 0.8-2.0 micron. Said zeolite exhibits superior hydrothermal stability in catalytic conversion of hydrocarbons. Especially, when said zeolite is applied in catalytic cracking of hydrocarbons, it will enhance the crackability of large molecules, improve gasoline octane value and stability, and reduce the sulfur content in the gasoline as well.

FIELD OF THE INVENTION

The present invention relates to a zeolite having MFI type structure.More particularly, the present invention relates to aphosphorus-containing zeolite having MFI type structure.

BACKGROUND OF THE INVENTION

Zeolite having MFI (structure symbol recommended by International Unionfor Pure and Applied Chemistry in 1978) type structure, such as ZSM-5developed by Mobil Oil Corporation since 1972, has been appliedextensively as a catalytic material to various hydrocarbon conversionreactions. With the development of new applications, extensive researchhas been carried out to improve its catalytic performance, besides itssynthesis method.

U.S. Pat. No. 3,972,832 discloses a phosphorus-containing zeolite whichhas been prepared by treating H-ZSM zeolite with a phosphorus-containingcompound solution and heating the above-mentioned system. The thusobtained zeolite contains 0.78-4.5 wt. % phosphorus. Said zeolite can beused as a catalyst for the conversion of paraffinic compounds,especially paraffinic hydrocarbons.

U.S. Pat. Nos. 4,374,294, 4,391,739 and 4,399,059 disclose a zeolitecatalyst composition containing phosphorus and a metal selected fromGroup IA and /or Group IIIA (Sc, Y, and RE) of the Periodic Chart of theElements. The process for preparing said composition comprisesimpregnating ZSM zeolites with an aqueous diammonium hydrogen phosphatesolution, and calcining them at a temperature of 400-700° C. in thepresence of 5-100% steam. Said zeolite catalyst exhibits goodpara-selectivity in the conversion of substituted aromatic compounds.

U.S. Pat. Nos. 4,356,338 and 4,456,780 relate to a method for extendingthe life of ZSM zeolite catalyst by treating the catalyst with aphosphorus containing compound to deposit 2-15 wt. % phosphorus on saidcatalyst. Then, said catalyst is calcined at 250-1000° C. in thepresence of 5-100% steam for 15 min. to 100 hours. Said method can alsobe carried out by treating the catalyst first with steam, then with aphosphorus containing compound.

U.S. Pat. No. 4,578,371 discloses a process for the manufacture of aphosphorus containing ZSM-5 zeolite, comprising mixing water, a silicondioxide source, an alkali metal hydroxide and an aluminum compound, andcrystallizing said mixture at a temperature of 95-230° C. withoutaddition of an organic compound, but in the presence of aluminumphosphate.

U.S. Pat. No. 4,605,637 discloses a method for enhancing the catalyticactivity of a low acidity zeolite, such as boron-containing ZSM-5zeolite or ZSM-5 zeolite with a silica/alumina ratio over 70, bycontacting said zeolite with an activating solution containing aneffective amount of aluminum phosphate at a temperature of 80-370° C.

U.S. Pat. No. 4,791,084 discloses a method for preparing a crackingcatalyst by mixing crystalline aluminosilicate particles and aluminaparticles having been impregnated with a phosphorus component. Saidcatalyst exhibits better metal poinsoning resistance, higher crackingactivity and improved gasoline selectivity in cracking of a heavy oil.

U.S. Pat. No. 5,080,878 relates to a process for reducing the surfaceactivity of ZSM-5 zeolite, by contacting said zeolite with an aqueousfluorosilicate salt, preferably (NH₄)₂ SiF₆, to substitute the aluminumatom by silicon atom. Therefore, the catalytic activity of said zeoliteis enhanced for a variety of hydrocarbon conversion reactions, inparticular, for the oligomerization of olefins to prepare a lube baseoil with high viscosity index.

U.S. Pat. No. 5,171,921 discloses a method for producing olefins whereinthe catalyst is treated by impregnating ZSM-5 zeolite having a Si/Alratio of 20-60 with a phosphorus-containing solution so as to render thezeolite to contain 0.1-10 wt. % phosphorus and steam-activating thezeolite at 500-700° C. under a pressure of 1-5 atm. for 1-48 hours. Saidsteam activation can also be effected by adding 1-50% (mole ratio) steaminto hydrocarbon feedstock during the conversion reaction. Said zeolitecan be used as an active component in converting olefin and/or paraffinto C₂ -C₅ light olefins.

U.S. Pat. No. 4,650,655 discloses a process for synthesizing ZSM-5zeolite by using zeolites other than ZSM-5 as seed crystals. It isreported in the patent that ZSM-5 zeolite with a relative crystallinityof 110% is synthesized by using NaY zeolite as seed crystals in thepresence of tetrapropyl ammonium bromide and crystallizing at 212° F.(100° C.) for 80 hours. (The relative crystallinity of said zeolite iscompared with the zeolite synthesized by using ZSM-5 zeolite as seedcrystals)

U.S. Pat. No. 5,232,675 discloses a rare earth-containing high-silicazeolite having penta-sil type structure. The anhydrous composition ofsaid zeolite can be defined by the formula xRE₂ O₃. y Na₂ O. Al₂ O₃.zSiO₂, wherein x=0.01-0.30, y=0.41.0, and z=20-60. Owing to the 24times higher normal hexane/cyclohexane adsorption ratio than that ofZSM-5 zeolite, the pore opening of said zeolite is narrower than that ofZSM-5 zeolite. Said zeolite is synthesized by well distributing the seedcrystals into a colloid system composed of water glass, an aluminiumsalt, an inorganic acid, and water, and then crystallizing at 130-200°C., preferably 160-190° C., for 12-60 hours, preferably for 16-30 hours.Said seed crystals are REY, REHY, or REX which contains rare earthelements 2-27% and sodium<7.0%(both based on the weight of oxides). Ascompared with the conventional ZSM-5 zeolite, said zeolite possesses ahigher catalytic activity and better hydrothermal stability.

U.S. Pat. No. 5,380,690 discloses a cracking catalyst for producinglower olefins, wherein a phosphorus and rare earth-containing highsilica zeolite having a structure of pentasil (P-ZRP) is used. SaidP-ZRP zeolite is prepared by treating the zeolite described in U.S. Pat.No. 5,232,675 with an aluminum phosphate sol, and then activating thezeolite in steam. More specifically, it is prepared by pre-exchangingthe zeolite with ammonium ion to reduce its sodium content to a level ofless than 0.1 wt. % (based on Na₂ O), then evenly mixing the zeolitewith an aluminum phosphate sol according to the weight ratio of aluminumphosphate sol (based on P2O₅): zeolite (dry base)=1:(5-99), followed bycalcining the mixture at 300-600° C. for 0.5-6 hours in the presence of10-100% steam. Said aluminum phosphate sol has a composition of Al₂ O₃:P₂ O₅ =1:(1-3). The thus-obtained zeolite has a phosphorus content of2-20 wt. %. Said zeolite catalyst exhibits better hydrothermalstability, improved bottom conversion and higher C₂ -C₅ light olefinsyields.

The mesopore of the zeolite plays an important role in improvingcatalytic performance, especially reaction capacity of large moleculesreactions. It has not been reported in the prior art that any MFI typezeolite possesses so large amount of mesopore in the range of 1.0-10 nm.

It is an object of the present invention to provide a highlyhydrothermal stable phosphorus containing MFI type zeolite, especiallyhaving a large amount of mesopore in the range of 1.0-10 nm. It is afurther object of this invention to provide a method for preparing saidzeolite.

SUMMARY OF THE INVENTION

The present invention provides a phosphorus containing MFI type zeolitehaving an anhydrous chemical composition of the formula (based on moleratios of oxides):

    0.01-0.3Na.sub.2 O.Al2O3.0.2-1.5P.sub.2 O.sub.5.30-90SiO.sub.2

Said zeolite possesses X-ray diffraction patterns listed in Table 1 anda pore volume ratio of 1.0-10 nm mesopore to 10-membered ring pore(0.5-0.6 nm) being no less than 0.5. The crystal particle size of saidzeolite is in the range of 0.8-2.0 micron.

The phosphorus containing MFI type zeolite of the present invention isprepared according to the following procedures: selecting a faujusitesuch as NaY, HY or NH₄ as seed crystals; adding said seed crystals to acolloid system composed of water glass, an aluminum salt, an inorganicacid, and water to carry out a crystallization reaction; ion-exchangingthe obtained crystalline product into NH₄ -form; dealuminating thezeolite by H₂ SiF₆ ; and activating the obtained zeolite with aphoshorus-alumina activating agent in the presence of steam at elevatedtemperature.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is the TEM micrograph of said zeolite prepared by Example 1.

FIG. 2 is the ³¹ P-MAS NMR spectrum of said zeolite prepared by Example1.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a phosphorus containing MFI type zeolitehaving an anhydrous chemical composition of the formula (based on moleratios of oxides):

    0.01-0.3Na.sub.2 O.Al.sub.2 O.sub.3.0.2-1.5P.sub.2 O.sub.5.30-90SiO.sub.2

Said zeolite possesses X-ray diffraction patterns listed in Table 1 anda pore volume ratio of 1.0-10 nm, preferably 3.0-5.0 nm mesopore to10-membered ring pore (0.5-0.6 nm) being no less than 0.5. The crystalparticle size of said zeolite is in the range of 0.8-2.0 micron.

The phosphorus containing MFI type zeolite according to the presentinvention possesses the following characteristics:

1. Said zeolite has an anhydrous chemical composition of the followingformula (based on mole ratios of oxides):

    0.01-0.3Na.sub.2 O.Al.sub.2 O.sub.3.0.2-1.5P.sub.2 O.sub.5.30-90SiO.sub.2

2. Said zeolite possesses X-ray diffraction data listed in Table 1. Thesymbols used in Table 1 represent the relative intensity in the XRDspectra:VS:80-100%; S:60-80%; M:40-60%; W:20-40%; VW:<20%.

                  TABLE 1    ______________________________________    X-ray diffraction pattern data of the zeolite of the present    invention           d/ × 10.sup.-1  nm                    I/I.sub.0    ______________________________________           10.01 ± 0.2                    M           6.56 ± 0.1                    VW           6.00 ± 0.1                    VW           4.27 ± 0.08                    VW           3.86 ± 0.07                    VS           3.82 ± 0.07                    S           3.76 ± 0.05                    W           3.72 ± 0.05                    W           3.65 ± 0.05                    W    ______________________________________

3. In the ²⁷ Al-MAS NMR spectrum of said zeolite, a peak at chemicalshift of 55-60 ppm is assigned to the Al(4Si) coordination (one AlO₄ islinked with four SiO₄), besides, another peak at about 40 ppm isassigned to the Al(4P) coordination (one AlO₄ is linked with four PO₄).In the ³¹ P-MAS NMR spectrum of said zeolite, a peak at about -29 ppm isdue to the P(4Al) coordination (i.e. an inter-reaction between PO₄ andadjacent AlO₄ exists.), as shown in FIG. 2. Based on the above results,it is assumed that the phosphorus atoms contained in said zeolite arechemically bonded with the Al atoms in the framework of the zeolite.

Furthermore, the phosphorus contained in said zeolite is evenlydistributed in the surface layer of said zeolite crystal. The results ofTransmission Electron Microscope (TEM)-Energy Diffraction Spectra (EDS)showed that the phosphorus content was nearly at the same level in thesurface layer of any crystal particles in said zeolite (Table 2).

                  TABLE 2    ______________________________________    P.sub.2 O.sub.5  contents(wt %) on the surface layer of crystal    particles    of randomly taken samples    ______________________________________    zeolite of the present                   1.87   1.88   1.90 1.89 1.87 1.90    invention, wt %    even mixture of zeolite                   2.48   0.92   1.01 3.14 0.05 0.02    ZSM-5 and AlPO.sub.4, wt. %    ______________________________________

4. The pore volume ratio of the mesopore ranging 1.0-10 nm in diameter,especially 3.0-5.0 nm in diameter to the 10-membered ring pore (porediameter of 0.5-0.6 nm) is no less than 0.5. This is a characteristic ofthe zeolite of the present invention. In the conventional ZSM-5 zeolitehaving the same structure, only 10-membered ring micropore (porediameter 0.5-0.6 nm) exists, whereas the zeolite of the presentinvention has a relatively large amount of mesopores as compared withthe conventional ZSM-5 zeolite.

5. The crystal particle size of said zeolite is in the range of 0.8-2.0micron.

Said phosphorus containing MFI type zeolite according to the inventionis prepared by the following procedures:

a. Crystallization: a seed crystal is dispersed homogeneously into acolloid system comprising of water glass, an aluminum salt, an inorganicacid, and water, and the thus obtained mixture is crystallized at130-200° C. for 10-60 hours. Said seed crystal can be one or more of thefollowing zeolites: NaY, NH₄ Y, HY, NaX or HX, preferably NH₄ Y and HY.The mole composition of said colloid system is as follows: SiO₂ /Al₂ O₃=30-100, Na₂ O/Al₂ O₃ =5-10, H₂ O/SiO₂ =15-50, the amount of Na₂ Oherein indicates the alkalinity of said system, not including the amountof Na₂ O neutralized by the acid.

Said water glass can be preheated to 60-100° C. before mixing with othercomponents so as to decrease the viscosity of the said colloid systemand the crystal particle size of said zeolite.

The amount of said faujusite seed crystals used should be such that themole ratio of Al₂ O₃ provided by the seed crystal to Al₂ O₃ provided byother components in said colloid system is in the range of 0.4-0.8.

Said aluminum salt is Al₂ (SO₄)₃, AlCl₃, or an aluminum salt ofphosphoric acid selected from for example AlPO₄, Al₂ (HPO₄)₃, and Al(H₂PO₄)₃.

Said inorganic acid is selected from phosphoric acid, sulfuric acid,hydrochloric acid, and nitric acid. The amount of the inorganic acidused should make the alkalinity of said reaction system in the range ofthe mole ratios of the colloid system.

b: Ammonium ion-exchange: said crystalline product in step a ision-exchanged with an aqueous ammonium salt solution according to theweight ratio of crystalline product: ammonium salt:H₂O=1:(0.2-1.0):(5-20) at 60-95° C. for 0.5-2 hours. Said ammonium saltcan be a conventional inorganic acid ammonium salt, such as (NH₄)₂ SO₄,NH₄ Cl, (NH₄)₃ PO₄, or NH₄ NO₃.

The amount of Na2O in NH₄ ⁺ -form crystalline product is normally lessthan 0.1 wt %.

c: Dealumination: said NH₄ ⁺ -form crystalline product in step b isdealuminated by reacting with an aqueous H₂ SiF₆ solution at 50-70° C.,for 1-5 hours, according to the weight ratio of NH₄ ⁺ -type crystallineproduct: H₂ SiF₆ :H₂ O=1:(0.05-0.3):(3-20).

The mole ratio of SiO₂ /Al₂ O₃ in the framework of said dealuminatedcrystalline product should be 35-90.

d: Activation: said dealuminated crystalline product in step c is evenlymixed with an

d: Activation: said dealuminated crystalline product in step c is evenlymixed with an activating agent containing phosphorus and aluminum (basedon P₂ O₅) according to the weight ratio of crystalline product : saidagent=1:(0.05-0.80), then the resulted mixture is calcined at 400-650°C., with 10-100% steam for 1-5 hours.

Said phosphorus-alumina activaing agent is composed of pseudo-boehmiteand phosphoric acid according to the mole ratio of Al₂ O₃ :P₂ O₅=1:(3-6).

As has heretofore been stated, a particular activating agent containingphosphorus and aluminum is used to treat the MFI type zeolite of theinvention according to a special procedure of the present invention. Thephosphorus in said phosphorus containing MFI type zeolite might bechemically bonded with the framework Al atom of the zeolite. Therefore,said zeolite exhibits superior hydrothermal stability than conventionalHZSM-5 zeolite. For example, after hydrothermal treatment at 800° C. in100% steam for 12 hours, the n-C₁₄ alkane cracking activity ofconventional zeolite HZSM-5 decreased from 90% to 35%, however, theactivity of the present zeolite was nearly the same as before treating.(cf Example 7)

The phosphorus containing MFI type zeolite of the present invention canbe used in all catalytic conversion processes in which conventionalZSM-5 can be used. Furthermore, owing to its large amount of mesopore inthe range of 1.0-10 nm, said zeolite is suporior for reactions involvinglarger molecules, e.g. in the catalytic conversion of heavy petroleumhydrocarbons, as compared to the conventional ZSM-5 zeolite. When saidzeolite, as an active component of cracking catalyst, is applied incatalytic cracking of hydrocarbons, it will enhance the crackability oflarge molecules, improve gasoline octane value and stability, and reducethe sulfur content in the gasoline products as well, as compared withconventional zeolite ZSM-5.

EXAMPLES

The present invention will be further described with reference to thefollowing samples. However, these examples are not to be construed tolimit the scope of the present invention.

In all the following examples and comparative examples, the chemicalcompositions of the zeolite product, such as Na₂ O, Al₂ O₃, and SiO₂were determined by chemical analysis; the P₂ O₅ content of said zeolitewas determined by X-ray fluorescence spectroscopy; X-ray diffraction(XRD) data of said zeolite was obtained with a Rigaku D/Max-IIIA X-raydiffraction apparatus (made in Japan) using the Cu--Kα radiation; thephosphorus content of the crystal surface layer was determined byscanning electronc microscope with microprobe analysis (TEM-EDS) method,using an integrated device of a JEOL JEM-2000 FXII high resolutionapparatus and a LINK QX-2000 Energy Spectra apparatus. The crystalparticle size of the zeolite was determined by ISI-60A SEM; ³¹ P-MAS NMRspectrum was obtained with a BRUKER AM-300 MAS apparatus; mesopore andmicropore (10-membered ring) volumes were determined by the lowtemperature nitrogen adsorption method, using the standard procedure ofASTM D-4641-87.

EXAMPLE 1

150 g (95% dry base) of HY zeolite having silica/alumina mole ratio of5.0 (manufactured by Catalyst Plant of Changling Petrochemical Works,Hunan province, China), was used as seed crystals and dispersed in 1300g of water glass (manufactured by Catalyst Plant of ChanglingPetrochemical Works) containing 3.5 wt. % Na₂ O and 11.0 wt. % SiO₂.1300 g of an aqueous Al₂ (SO₄)₃ solution containing 2.5 wt. % Al₂ O₃ wasadded to the above mixture while stirring. An aqueous 20 wt. % H₂ SO₄solution was used to adjust the pH of the above system making it into acolloidal state at pH 11.5. The prepared colloid was crystallized at180° C. for 16 hours. After filtration and washing, the crystallineproduct was obtained.

1000 g (dry base) of the above-prepared crystalline product wasion-exchanged with 6250 g of an aqueous 8 wt. % ammonium sulfatesolution for 1 hour at 60° C. while stirring. After filtration andwashing, the NH₄ ⁺ -form crystalline product was obtained.

100 g (dry base) of said NH₄ ⁺ -form crystal was dealuminated byreacting with 1600 g of an aqueous 0.5 wt. % H₂ SiF₆ solution at 50° C.for 5 hours while stirring, then followed by filtration and washing.

Said dealuminated crystalline product was evenly mixed with 40 g of H₂ Oand 8.4 g of phosphorus-alumina activating agent, composed ofpseudo-boehmite (manufactured by Shandong Aluminum Works, China) and H₃PO₄, containing 4.4 wt. % Al₂ 0₃ and 30.0 wt. % P₂ O₅, followed bydrying at 120° C. for4 hours, then activated at 600° C. for 1.5 hours inthe presence of 100% steam. The obtained product was the zeoliteprovided by the present invention.

Said zeolite had an anhydrous chemical composition (based on mole ratiosof the oxides, same for the following examples) as follows:

    0.09Na.sub.2 O.Al.sub.2 O.sub.3.0.36P.sub.2 O.sub.5.35.0SiO.sub.2

Said zeolite possesses X-ray diffraction pattern data as listed in Table3. The surface P₂ O₅ content in 5 crystal particles taken randomly fromsaid zeolite was 2.2 wt. %, 2.6 wt. %, 2.5 wt. %, 2.6 wt. %, and 2.4 wt.%, respectively (The P₂ O₅ content was determined by TEM-EDS method).The TEM micrograph of said zeolite was shown in FIG. 1 (The crystalparticle size was about 1 micron). The ³¹ P-MAS NMR spectra of saidzeolite was shown in FIG. 2. The mesopore (3.2-4.9 nm) volume was 0.18ml/g, and the micropore (10-membered ring, the MPD was about 0.5nm)volume was 0.165 ml/g.

                  TABLE 3    ______________________________________    X-ray diffraction pattern data of the zeolite of the present    invention           d/ × 10.sup.-1  nm                   I/I.sub.0, × 100    ______________________________________           11.18   37           10.01   40           6.37    7           6.00    11           5.71    9           5.58    9           5.05    6           4.98    8           4.62    6           4.37    7           4.27    12           4.01    7           3.86    100           3.82    72           3.76    36           3.72    39           3.65    26           3.49    6           3.44    12           3.35    9           3.31    11           3.05    12    ______________________________________

EXAMPLE 2

1.0 liter of water glass (manufactured by Catalyst Plant of ChanglingPetrochemical Works, containing 250.4 g/l SiO₂ ; 78.4 g/l Na₂ O; d₄ ²⁰1.25) was heated to 80° C. 21.0 g of NH₄ Y zeolite (manufactured byCatalyst Plant of Changling Petrochemical Works, with silica/aluminamole ratio of 5.0, 90% dry base) was well dispersed into the above waterglass while stirring. Then, an aqueous acidic Al₂ (SO₄)₃ solutionconsisting of 76.5 ml of aqueous an Al₂ (SO₄)₃ solution(containing 92.7g/l Al₂ O₃, d₄ ²⁰ 1.198,) and 175.7 ml of an aqueous 26.0 wt. % H₂ SO₄solution (d₄ ²⁰ 1.192) was added into the above-heated water glasssolution while stirring, and reacted. Said reaction mixture wascrystallized at 180° C. for 15 hours, followed by filtration andwashing, the crystalline product was obtained.

100 g (dry base) of said crystalline product was ion-exchanged with 2000g of an aqueous 3.0 wt. % (NH₄)₂ SO₄ solution at 90° C. for 2 hours withstirring followed by filtration and washing. The obtained NH₄ ⁺ -formcrystalline product was then dealuminated by reacting with 1000 g of anaqueous 1.25 wt. % H₂ SiF₆ solution at 70° C. for 3 hours whilestirring, followed by filtration and washing. Said dealuminatedcrystalline product was evenly mixed with 70 g of H₂ O and 16.8 g ofphosphorus-alumina activating agent, composed of Al(OH)₃ powder and H₃PO₄, containing 1.45 wt. % Al₂ O₃ and 12.0 wt. % P₂ O₅, followed bydrying at 110° C. for 5 hours, then activated at 550° C. for 2.0 hoursin the presence of 100% steam. The obtained product was the zeoliteprepared by the present invention.

The X-ray diffraction pattern data, the crystal particle size and the ³¹P-MAS NMR spectrum data of the above said zeolite were similar to thedata shown in Table 3, FIG. 1 and FIG. 2, respectively. Said zeolite hadan anhydrous chemical composition as follows:

    0.05Na.sub.2 O.Al.sub.2 O.sub.3.0.65P.sub.2 O.sub.5.52SiO.sub.2

The surface P₂ O₅ contents of 3 crystal particles taken randomly fromsaid zeolite were 2.78 wt. %, 2.86 wt. %, and 2.75 wt. %, respectively.The mesopore (3.0-4.5 nm) volume was 0.08 ml/g, and the micropore(10-membered ring, with MPD about 0.5 mn) volume was 0.14 ml/g.

EXAMPLE 3

140 g of NaY zeolite was well dispersed in 5.2 liter of water glass(same as used in Example 2), having been heated to 100° C. whilestirring. Then, the aqueous acidic Al₂ (SO₄)₃ solution consisting of 458ml of an aqueousn Al₂ (SO₄)₃ solution (same as used in Example 2) and804 ml of an aqueous dilute H₂ SO₄ solution(same as used in Example 2)was added into the above-heated water glass solution while stirring. Theobtained colloid was crystallized at 190° C. for 11 hours, followed byfiltration and washing. 185 g (dry base) of said crystalline product wasion-exchanged with 1800 g of an aqueous 4.0 wt. % (NH4)₂ SO₄ solution at80° C. for 4 hours while stirring. After filtration, the filter cake wasthen dealuminated by reacting with 925 g of an aqueous 3.2 wt. % H₂ SiF₆solution at 90° C. for 1 hour while stirring, followed by filtration andwashing. Said filter cake was evenly mixed with 90 g of H₂ O and 37.3 gof phosphorus-alumina activating agent, composed of pseudo-boehmite andH₃ PO₄, containing 5.0 wt. % Al₂ O₃ and 25.0 wt. % P₂ O₅, followed bydrying at 100° C. for 6 hours, then activated at 500° C. for 3.0 hoursin the presence of 100% steam. The obtained product was the zeoliteprovided by present invention.

The X-ray diffraction pattern data, the crystal particle size and the 31p MAS NMR spectrum data of the above said zeolite were similar to thedata shown in Table 3, FIG. 1 and FIG. 2, respectively. Said zeolite hadan anhydrous chemical composition as follows:

    0.03Na.sub.2 O.Al.sub.2 O.sub.3.0.69P.sub.2 O.sub.5.60SiO.sub.2

The surface P₂ O₅ content of 3 crystal particles taken randomly fromsaid zeolite was 2.50 wt. %, 2.49 wt. %, and 2.57 wt. %, respectively.The mesopore (3.5-4.7 nm) volume was 0.08 ml/g, and the micropore(10-membered ring, with MPD about 0.5 nm) volume was 0.150 ml/g.

EXAMPLE 4

180 g of HX zeolite having a silica/alumina mole ratio of 3.0 (90% drybase, manufactured by Nanjing Inorganic Chemical Plant, China) was welldispersed in 10.0 liter of water glass (same as used in Example 2, atambient temperature) while stirring. Then, the aqueous acidic Al₂ (SO₄)₃solution consisting of 765.0 ml of an aqueous Al₂ (SO₄)₃ solution (d₄ ²⁰1.198, 92.7 g/l Al₂ O₃) and 1757.0 ml of an aqueous 26.0 wt. % dilute H₂SO₄ solution(d₄ ²⁰ 1.192) was added into the above-heated water glasssolution with stirring. Said reaction mixture was crystallized at 170°C. for 20 hours, followed by filtration and washing, the crystallineproduct was obtained.

100 g (dry base) said crystalline product was ion-exchanged with 2000 gof an aqueous 4.0 wt. % NH₄ Cl solution at 70° C. for 4 hours whilestirring. After filtration, the NH₄ ⁺ -form filter cake was thendealuminated by reacting with 1000 ml of an aqueous 1.25 wt. % H₂ SiF₆solution at 95° C. for 3 hour while stirring, followed by filtration andwashing.

Said filter cake was evenly mixed with 80 g of H₂ 0 and 25.1 g ofphosphorus-alumina activating agent, composed of pseudo-boehmite and H₃PO₄, containing 3.0 wt. % Al₂ O₃ and 12.5 wt. % P₂ O₅, followed bydrying at 120° C. for 6 hours, then activated at 450° C. for 5.0 hoursin the presence of 100% steam. The obtained product was the zeoliteprepared by the present invention. Said zeolite had an anhydrouschemical composition as follows:

    0.04Na.sub.2 O.Al.sub.2 O.sub.3.0.75P.sub.2 O.sub.5.80SiO.sub.2

The X-ray diffraction pattern data and the ³¹ P-MAS NMR spectrum data ofthe above zeolite were similar to the data shown in Table 3 and FIG. 2,respectively. The average crystal particle size was about 1.8 microndetermined by SEM. The surface P₂ O₅ content of 3 crystal particlestaken randomly from said zeolite was 3.24 wt. %, 3.42 wt. %, and 3.30wt. %, respectively. The mesopore (3.7-5.0 nm) volume was 0.082 ml/g,and the micropore (10-membered ring, with MPD about 0.5 nm) volume was0.157 ml/g.

EXAMPLE 5

205 g of NH₄ ⁺ - form crystalline product as prepared in Example 1, wasdealuminated by reacting with 1640 g of an aqueous 2.5 wt. % H₂ SiF₆solution at 70° C. for 3 hours while stirring, followed by filtrationand washing. Said filter cake was evenly mixed with 80 g of H₂ 0 and30.5 g of phosphorus-alumina activating agent, composed ofpseudo-boehmite and H₃ PO₄, containing 4.4 wt. % Al₂ O₃ and 14.0 wt. %P₂ O₅, followed by drying at 150° C. for 2 hours, then activated at 600°C., in self-steaming condition for 2.0 hours. The obtained product wasthe zeolite prepared by the present invention. Said zeolite had ananhydrous chemical composition as follows:

    0.06Na.sub.2 O.Al.sub.2 O.sub.3.0.80P.sub.2 O.sub.5.70SiO.sub.2

The X-ray diffraction pattern, data the crystal particle size and the ³¹P-MAS NMR spectrum data of the above said zeolite were similar to thedata shown in Table 3, FIG. 1 and FIG. 2, respectively. The surface P₂O₅ content of 3 crystal particles taken randomly from said zeolite was2.10 wt. %, 2.49 wt. %, and 2.52 wt. %, respectively. The mesopore(3.5-4.2 nm) volume was 0.16 ml/g, and the micropore (10-membered ring,with MPD about 0.5 nm) volume was 0.14 ml/g.

EXAMPLE 6

115 g (dry base) of NH₄ ⁺ - from crystalline product as prepared inExample 1, was dealuminated by reacting with 700 g of an aqueous 4.6 wt.% H₂ SiF₆ solution at 80° C. for 2.5 hours while stirring, followed byfiltration and washing. Said filter cake was evenly mixed with 50 g ofH₂ O and 34.8 g of phosphorus-alumina activating agent, composed ofaluminum hydroxide and H₃ PO₄, containing 1.0 wt. % Al₂ O₃ and 7.0 wt. %P₂ O₅, followed by drying at 120° C. for 4 hours, then activated at 400°C. for 4.0 hours in the presence of 100% steam. The obtained product wasthe zeolite prepared by the present invention. Said zeolite had ananhydrous chemical composition as follows:

    0.04Na.sub.2 O.Al.sub.2 O.sub.3.0.87P.sub.2 O.sub.5.90SiO.sub.2

The X-ray diffraction pattern data, the crystal particle size and the ³¹P-MAS NMR spectrum data of the above said zeolite were similar to thedata shown in Table 3, FIG. I and FIG. 2, respectively. The surface P₂O₅ content of 3 crystal particles taken randomly from said zeolite was1.90 wt. %, 2.10 wt. %, and 2.23 wt. %, respectively. The mesopore(3.2-4.5 nm) volume was 0.12 ml/g, and the micropore (10-membered ring,with MPD about 0.5 nm) volume was 0.150 ml/g.

Comparative Example 1

The corresponding conventional ZSM-5 zeolite (produced by the CatalystPlant of Qilu Petrochemical Corp., China, ethyl amine as template) wasprepared according to the method as described in Petroleum Processing(Chinese), No.11-12, p.88, 1978. Said conventional zeolite ZSM-5 wasion-exchanged with an aqueous (NH₄)₂ (SO₄)₃ solution under the sameconditions as described in Example 1. The filter cake was then calcinedat 560° C. for 2 hours. The obtained product had an anhydrous chemicalcomposition as follows:

    0.04Na.sub.2 O.Al.sub.2 O.sub.3.60SiO.sub.2

The mesopore (3.0-5.0 nm) volume was 0.02 ml/g, and the micropore(10-membered ring, with MPD about 0.5 nm) volume was 0.169 ml/g.

EXAMPLE 7

This example shows the hydrothermal stability of the zeolite prepared bythe present invention.

The zeolite samples prepared in Example 1 and Comparative Example 1 weretreated and aged in 100% steam at 800° C. for 1, 4, 8 and 12 hours,respectively. Said aged zeolite samples were then tested in a pulsereactor at 480° C., using n-C₁₄ alkane as feedstock to evaluate crackingactivity, wherein activity=(1-fraction of unconverted n-C₁₄)×100%. Thedosage of n-C14 alkane was 0.5 μl, and 0.1 g of the zeolite sample wasloaded in the reactor. The results were listed in Table 4. It can beseen that the hydrothermal stability of the zeolite of the presentinvention is significantly higher than that of the correspondingconventional ZSM-5.

                  TABLE 4    ______________________________________    Aging Time   n-C.sub.14  cracking activity    (hr.), 800° C.                 Example 1                          Comparative Example 1    ______________________________________    1            99       90    4            99       70    8            99       50    12           98       35    ______________________________________

EXAMPLE 8

This example shows the heavy oil cracking performance of the zeolite ofthe present invention.

Zeolite samples prepared in Example 1 or Comparative Example 1 (A),REUSY (Rare Earth exchanged Ultrastable Y type zeolite, manufactured byCatalyst Plant of Changling Petrochemical Works, designated as B),kaolin (C) and pseudo-boehmite (D) were mixed according to the weightratio of A:B:C:D=15:10:56:19, homogenized and spray-dried to obtain twocatalysts labeled as Cat-1 and Ref-1, respectively.

The prepared catalysts were treated at a temperature of 800° C. for 4hours in the presence of 100% steam, and then tested in afixed-fluidized bed reactor in order to compare the differences betweenthe two catalysts in increasing gasoline octane value and decreasingsulfur content of gasoline. Before evaluation, the two catalysts werewell mixed, according to a weight ratio of 85:15, with a commercialequilibrium catalyst SRNY (taken from the Resid FCC Unit of ChanglingPetrochemical Works), respectively. The two well-mixed catalysts werethen evaluated under reaction conditions: 500° C., cat/oil ratio 3.0 andWHSV 20.0 h-¹. The feedstock used was a blend of VR and VGO according toa weight ratio of VR: VGO =20:80. The properties of the feedstock werelisted in Table 5. The evaluation results were listed in Table 6. Thedata listed in Table 6 indicate that as compared with the conventionalHZSM-5 zeolite, the zeolite of the present invention exhibits superiorheavy oil crackability, better performance in increasing gasoline octanevalue and decreasing sulfur content in the gasoline and improvedinduction period of the gasoline as well.

                  TABLE 5    ______________________________________    Feed Properties    ______________________________________    IBP, ° C.  224    50 v % BP, ° C.                      460    d.sub.20,g · ml.sup.-1                      0.8995    viscosity, cP(80° C.)                      20.4    Freezing Point, ° C.                      41    Carbon Residue, wt. %                      2.17    Heavy Metals, ppm    Na                1.7    Fe                2.0    Ni                1.7    V                 0.1    Cu                <0.1    ______________________________________

                  TABLE 6    ______________________________________                SRNY       Eq. Cat. plus                                     Eq. Cat. plus    Catalyst    Eq. Cat.   Cat-1     Ref.-1    ______________________________________    Conversion, wt %                65.93      70.89     69.45    Product yields, wt. %    Hydrogen    0.15       0.15      0.16    C.sub.1 ˜C.sub.2                1.24       1.59      1.45    C.sub.3 ˜C.sub.4                12.23      19.26     15.87    Gasoline (C.sub.5 ˜221° C.)                45.28      43.59     43.62    LCO(221˜330° C.)                19.98      18.80     19.06    Heavy Oil(>330° C.)                14.09      10.30     11.47    Coke        7.04       8.31      8.38    Gasoline RON(c)                88.2       90.6      89.3    MON(c)      78.03      80.3      79.2    Gasoline Induction                463        620       100    Period (min)    Gasoline Sulfur                215        143       200    Content (ppm)    ______________________________________

What we claim is:
 1. A phosphorus-containing zeolite having MFIstructure, having an anhydrous chemical composition based on mole ratiosof oxides of the formula:

    0.01-0.3Na.sub.2 O.Al.sub.2 O.sub.3.0.1-1.5P.sub.2 O.sub.5.30-90SiO.sub.2 ;

possessing a X-ray diffraction pattern data listed in Table 1; andhaving the pore volume ratio of 1.0-10 nm mesopore to 10-membered ringpore being no less than 0.5.
 2. A zeolite according to claim 1, whereinthe pore volume ratio of 3.0-5.0 nm mesopore to 10-membered ring pore insaid zeolite is no less than 0.5.
 3. A zeolite according to claim 1,wherein said zeolite is characterized in a peak at about 40ppm (chemicalshift) in ²⁷ Al-MAS NMR spectrum and a peak at about -29 ppm in ³¹ P-MASNMR spectrum.
 4. A zeolite according to claim 1, wherein the crystalparticle size of said zeolite is in the range of 0.8-2 micron.
 5. Aprocess for preparing the zeolite according to claim 1, comprising thesteps of crystallizing a reaction system comprising an aluminum salt, aninorganic acid, water and a seed crystal selected from a Na⁺, H⁺ or NH₄⁺ -form faujusite; ion-exchanging the crystalline product into NH₄ ⁺-form; dealuminating the NH₄ ⁺ -form crystalline product with H₂ SiF₆ ;and activating the dealuminated crystalline product by an activationagent containing phosphorus and aluminum at elevated temperature in thepresence of steam.
 6. A process according to claim 5, wherein saidcrystallizing step comprises the steps of dispersing the seed crystal ofNaY, NH₄ Y, NaX or HX into a mixture comprising an aluminum salt, aninorganic acid, water and water glass preheated to 60-100° C. to resultin a colloid system with mole ratios of SiO₂ /Al₂ O₃ =30-100, Na₂ O/Al₂O₃ =5-10, H₂ O/SiO₂ =15-50 and crystallizing said colloid system at130-200° C. for 10-60 hours.
 7. A process according to claim 6, whereinsaid seed crystal is zeolite NH₄ Y or HY.
 8. A process according toclaim 5 or 6, wherein said aluminum salt is selected from Al₂ (SO₄)₃,AlCl₃, AlPO₄, Al₂ (HPO₄)₃ or Al(H₂ PO₄)₃.
 9. A process according toclaim 5 or 6, wherein said inorganic acid is selected from H₂ SO₄, H₃PO₄, HCl, or HNO₃.
 10. A process according to claim 5, wherein said ionexchange step is carried out according to the weight ratio ofcrystalline product:inorganic ammonium salt:water= 1:(0.2-1.0):(5-20) ata temperature of 60-95° C. for 0.5-2 hours.
 11. A process according toclaim 10, wherein said inorganic ammonium salt is selected from (NH₄)₂SO₄, NH₄ Cl, or (NH₄)₃ PO₄.
 12. A process according to claim 5, whereinsaid dealuminating step is carried out according to the weight ratio ofNH₄ ⁺ -form crystalline product:H₂ SiF₆ :water=1:(0.050.30):(3-20) at atemperature of 50-70° C. for 1-5 hours.
 13. A process according to claim5, wherein said activating step is carried out by evenly mixing thedealuminated crystalline product with an activating agent containingphosphorus and aluminum, according to the weight ratio of dealuminatedcrystalline product:activating agent (based on P₂ O₅)=1:(0.05-0.80),followed by calcining at 400-650° C., in the presence of 10-100 % steamfor 1-5 hours.
 14. A process according to claim 13, wherein saidactivating agent containing phosphorus and aluminum is composed ofpseudo-boehmite and phosphoric acid according to the mole ratio of Al₂O₃ : P₂ O₅ =1:(3-6).